1. Field of Invention
The present invention relates to bearing defect detectors and in particular to an acoustic system for detecting defects in the bearings of moving railroad cars.
2. Description of the Prior Art
Heretofore, the detection of defects in railway car bearing has relied upon stationary infrared sensing means along railroad tracks to detect an abnormal heat rise associated with bearing failure in passing railroad cars. While such systems have enjoyed widespread use and an industry-wide reputation for reliability, they suffer from a serious drawback in that they detect a defect only after a damaging heat build-up has occurred within the bearing. Furthermore, this heat build-up often does not occur until a total bearing failure is imminent, thereby normally warranting an immediate stopping of the train so that an emergency field repair may be done. As this requires a delay in the train until a repair team may arrive with the necessary equipment, the total cost of this procedure can be very high.
From U.S. Pat. No. 4,790,190 and pending U.S. patent application Ser. No. 168,975 filed on Mar. 16, 1988, now U.S. Pat. No. 4,843,885, it is known that defects in tapered roller bearings, such as those used in railroad cars, produce sounds, during operation, at characteristic frequencies dependent upon the location or type of defect (i.e., at bearing cup, cone, or roller), the combination of the size of the wheel and the bearing capacity (frequently encountered combinations on railroads are a 28 inch wheel with a 70 ton capacity bearing, a 33 inch wheel with a 70 ton capacity bearing, and a 36 inch wheel with a 100 ton capacity bearing), and the speed of the train (which, of course, for a given diameter of the wheel, is proportional to the rotational frequency of the wheel). Additionally, irregularities in the wheel circumference ("flats") produce a characteristic frequency dependent upon wheel rotational frequency.
Thus, for any given train speed, a defective bearing will produce a sound at one of nine characteristic frequencies dependent upon the location of the defect in the bearing and the combination of the train speed, wheel size and bearing capacity. Wheel flats will produce a sound at one of three additional characteristic frequencies. Ideally, one need only listen for and detect the characteristic sound frequencies to determine the condition of the bearings of the passing train.
Unfortunately, railroad trains operate in extremely noisy environments. Train noises (such as wheel/rail rubbing, flange/rail squeal, loose equipment and cargo sounds, carbody noises, and clacking of rail joints for track circuits) and a wind "swish" are low-frequency sounds which tend to camouflage the impact frequencies produced by a defective bearing. Thus, while the production of characteristic impact frequencies in a moving bearing have been known, it has heretofore been impossible to isolate the impact frequencies in a meaningful manner so as to provide useful and reliable information. More importantly, the background noise may trigger defective bearing alarms and it thus becomes important to be able to distinguish between true defective bearing alarms and alarms set off by this background noise.